Tungsten coated glass fiber

ABSTRACT

A composite fiber adapted for usage as a resistively heated substrate in a continuous boron deposition process is described. The fiber has a glass filamentary core provided with a uniform continuous coating of tungsten, the glass core having a coefficient of thermal expansion of 3.5 to 5.0 X 10 6 in./in./* C so as to match that of the tungsten.

Bourdeau Jan. 22, 19741 TUNGSTEN COATED GLASS FIBER 3,215,555 Il/l965Krey 117/12313 3,669,724 6/1972 Brand [75] Inventor: Romeo BmrdeauWaPPmg 3,543,386 12/1970 Inoue et a] 117 107.2 Colm- 2,812,272 11/1957Nack et a1. 117/107.1 [7 Assigneez United Aircraft Corporation East3,506,464 4/1970 Baak 61 a1 106/54 Hartford, Conn.

[22] Filed: Nov. 11, 1971 Primary ExaminerA1fred L. Leavitt AssistantExaminer-J. Massie [21 1 Appl' 197913 Attorney, Agent, or Firm-John D.De] Ponti Related [15. Application Data [63] Continuation-impart of Ser.No. 864,839, Oct. 8,

1969, abandoned,

[57] ABSTRACT [52] US. Cl 117/227, 1l7/107.l, 1l7/107.2,

117/126 GM, 117/229 A composite fiber adapted for usage as a resistively[51 Int. Cl. B44a 1/02 heated substrate in a continuous boron depositionpro- [58] Field of Search 117/107.1, 106, 126, 217, 227, cess isdescribed. The fiber has a glass filamentary 117/107, 107.2 R, 123 B,126 GM, 201; core provided with a uniform continuous coating of 106/54;161/175 tungsten, the glass core having a coefficient of thermalexpansion of 3.5 to 5.0 X 10"- in./in./ C so as to [56] References Citedmatch that of the tungsten.

UN1TED STATES PATENTS 3,083,550 4/1963 Auerbach 117/126 GM 1 Claim, 1Drawing Figure y 1 7 WA 25mm! s v/y/s r /s A /i O y/V/V/V/Vfi we? 7 Ozzmy 9 I flIM/M fiZ Zg fifl/WP 5 f/ WMA PATENTED JAN 2 2 I974 TUNGSTENCOATED GLASS FIBER BACKGROUND OF THE INVENTION of tungsten on afilamentary glass substrate and the produce made thereby.

It is known that filamentary boron may be produced by a process whereinboron is chemically deposited on a resistively heated tungsten substratewhich is drawn through a gaseous reactant stream consisting of borontrichloride admixed with hydrogen. The boron fibers thus produced havebeen recognized as being admirably adapted for usage in fiber-reinforcedstructural composites, particularly in aerospace applications.Unfortunately, actual usage of boron fiber has been somewhat limited;primarily because of the prohibitive costs of production of such fibersin processes which use the expensive tungsten as a substrate for theboron.

Because of tungstens desirable electrical characteristics, compatibilitywith boron and overall ability to consistently produce quality boronfiber in conven-.

SUMMARY OF THE INVENTION The present invention relates to the productionof filamentary material suitable for use as a substrate in those borondeposition processes such as those shown in U. 5. Pat. No. 3,409,469,3,549,424 and 3,574,649 wherein the substrate is resistively heated. Inparticular, the invention contemplates a process wherein a uniformcoating of tungsten is continuously deposited on a glass filament ofselected characteristics. The use of glass filament as a substrate isfound to be highly advantageous since it presents a microscopicallysmooth surface, a circular cross section and can be drawn at extremelyhigh rates.

In a preferred embodiment, a glass filament having a coefficient ofthermal expansion of 3.5 to 5.0 X 10 in./in./C is passed through areactor heated to 900l,200 C and containing a reactant atmosphere untilthe desired depth of deposit of tungsten is obtained. The reactantatmosphere is preferably established of a tungsten halide admixed withhydrogen, the tungsten hexachloride and hydrogen being in a volume ratiorange of from V3 to l/l5 and at a pressure of from I to 20 mm Hg.

BRIEF DESCRIPTION OF THE DRAWING In the detailed description whichfollows, it will be convenient to make reference to the drawing whichshows, in a cross-sectional elevation, a reactor apparatus suitable foruse inthe practice of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring tothe drawing, ahorizontal reactor may be seen to comprise an elongated reactor tube 12,preferably of quartz, having enlarged enclosures 14 and 16 at oppositeends. Suitably received within the enclo sures I4 and 16, respectively,are a supply spool l8 and a take-up spool 20, aligned to axially pass aglass filament 22 through the reactor tube 12. The filament is heatableby suitable heating means such as a resistance sound heater coil 23.

A reactant gas inlet tube 24, located adjacent the wire inlet end of thereactor, is connected by separate lines 26 and 28 to a hydrogen source30 and a chlorine source 32. The lines 26 and 28 are each provided witha flow meter for control purposes. As seen in the drawing, the line 28provides chlorine gas upwardly through the bottom of a nickel crucible34 filled with tungsten powder and platinum catalyst located in theinlet tube 24. The crucible is of reduced diameter in comparison to theinlet tube 24 to allow flow of the hydrogen gas past adjacent wallsthereof. It will be appreciated that tungsten hexachloride is thuscontinuously produced in a controlled manner by a direct chlorination ofthe tungsten powder. It has been found that the present process issuccessful in producing satisfactory filaments when the reaction chamberis provided with tungsten hexachloride and'hydrogen in a volume ratiorange of /a to l/l5 with the most preferable ratio being 1/l0.

In order to promote the production of the tungsten hexachloride, theinlet tube is heated to a temperature of from 400550 C by suitableheating means such as resistance coil 40.

An outlet tube 36 is located adjacent the wire outlet end of thereactor. The outlet tube 36 is connected to a vacuum pump 38 for exhaustpurposes as well as for maintaining the desired subatmospheric pressurein the reactor. In the present process, reduced pressure has been foundnecessary and the preferred pressure range is l to 20 mm of mercury.

Satisfactory coatings of tungsten on glass by deposition from tungstenhexachloride-hydrogen can be made by maintaining the temperature of thereaction tube at 900-l,200 C and preferably at 1,000 C. Generallyspeaking, it is desirable to limit the residence time of the glassfilament in the reactor from 2 to 45 seconds, and preferably from 4 to 6seconds. In this way, a uniform coating of suitable thickness isdeposited without the glass substrate reaching its softeningtemperature. Experiments were made with filament speeds up to 2,000feet/hour. The optimum electrical resistance of the tungsten coatedglass will depend on its specific application, however, and theformation of a tungsten coating with an electrical resistance in therange from to 200,000 ohms has been found suitable for mostapplications.

Suitable glass substrates 22 may be generally classified as the SiOaluminum silicate and borosilicate glasses having a coefficient ofthermal expansion of 3.5 to 5 X 10 in./in./C and a softening pointbetween 800-920 C. It is important to note that the coefficient ofthermal expansion of the filamentary glass substrate is critical andmust substantially match that of the tungsten coating (4.3 X 10in./in./C). If outside the range specified, when subjected to heatingsuch as the resistive heating of the boron deposition process, theglasstungsten composite will be destroyed. If the'glass has acoefficient of thermal expansion below 3.5 X 10, the thermal mismatchcauses the tungsten to crack. If above the 5.0 X 10 upper limit, themismatch results in spalling off of the tungsten.

Examples of commercially available glasses which are suitable includethe Coming Glass Works No. 1720 series, such as No. 1716, G. E. GlassDesignation Nos. 175 and 177 and Owens Corning E-glass, D-glass andM-glass. Experiments were run using glasses having diameters from 0.81.0 mil. The formation of tungsten coated glass for usage as a substratein the production of boron or silicon carbide filaments results in anend product of reduced density. For example, a 1 mil tungsten coatedglass substrate reduces the density of a 4 mil boron filamentconventionally produced on 0.5 mil tungsten fiber from 2.7 to 2.4 gms/ccand it reduces the density ofa 2.2 mil boron filament (containing 80volume percent boron) from 3.2 to 2.45 gms/cc. In like manner, a 4 milSiC filament has a density reduced from 3.5 to 3.3 gms/cc while a 2.2mil fiber is reduced from 4.04 to 3.1 gms/cc. Besides the advantageousreduction in density, the present process is calculated to be one-tenththe cost per unit length.

EXAMPLE I resistance of 400 ohms/inch.

EXAMPLES ll and Ill The apparatus and process parameters of Example lare used, respectively, on filamentary G. E. Glass Nos. 175 and 177 toprovide a continuous and uniform coating of tungsten thereon.

EXAMPLES IV VI The apparatus and process parameters of Example I areused on respectively E-. D- and M-type filaments (commercially availablefrom Owens Coming) to provide a continuous and uniform coating oftungsten thereon.

What has been set forth above is intended primarily as exemplary toenable those skilled in the art in the practice of the invention and itshould be therefore understood that, within the scope of the appendedclaims, the invention may be practiced in other ways than asspecifically described.

What is claimed is:

l. A composite fiber adapted for usage as a resistively heated substratein a continuous boron deposition process comprising a glass filamentarycore having a coefficient of thermal expansion within the range of 3.5to 5.0 X 10 in./in./C and a uniform continuous coating of tungsten onsaid glass filamentary core, said coating being sufficiently thick toestablish an electrical resistance in the composite fiber of to 200,000ohms. =l

